The prime objective of this project is to develop an understanding of the fundamental chemistry of metal ions utilized in radioimmunotherapy, especially lead and bismuth. To accomplish this objective, we need to learn the coordination chemistry of metal ions, in particular, their kinetic and thermodynamic behaviors in solution. This information can then be used to develop radiolabeled antibody systems for use in therapy. Substantial progress was made in obtaining Bi-213 from an Actinium-225 generator. Yield of up to 10 mCi were obtained and purified to use in labeling antibodies. However, it was observed that after a few days, radiolysis of the resin in the generator caused loss of yield. studies have been initiated to solve this problem by employing more stable resin bases.